Image forming apparatuses, for recording images on recording mediums such as paper or the like, for example, inkjet printers with inkjet heads (corresponding to recording heads), have been conventionally known. In the inkjet printer, the image is formed (printed) on the recording medium, e.g. paper or the like, which is placed on a transfer belt wound around at least two transfer rollers, in an image forming area. The transfer rollers are driven by a driving roller, and the transfer belt is moved cyclically by the transfer rollers. Subsequently, the recording medium, e.g. paper or the like, which is placed on the transfer belt, is transferred to the image forming area facing the inkjet head, and the image is formed on the recording medium. The recording medium is discharged thereafter.
In the case of such image forming apparatus provided with a conveying mechanism that comprises the aforementioned transfer belt and transfer rollers, for example, the parallelism of rotational axes of the transfer rollers or the external diameters thereof may vary during the manufacture. As a result, the transfer belt may meander and be positionally deviated in the width direction when the transfer belt is being transferred.
If the transfer belt is positionally deviated in this manner, such problems occur that the recording medium transferred by the transfer belt is positionally deviated, and that the image forming position on the recording medium is also positionally deviated.
Heretofore, the configuration as described below in the Patent Document 1 has been known. In the configuration, a detective device for detecting the displacement of the transfer belt in the width direction is provided, and one of the transfer rollers wound around by the transfer belt is axially displaced based on detective signals from the detective device, thereby inhibiting the positional deviation of the transfer belt. In this configuration, the positional deviation is suppressed in the portion of the transfer belt which is engaged with the axially displaced transfer roller.
Moreover, the configuration as described below in the Patent Document 2 has been known. In the configuration, a circular engaging plate is attached to a rotational axis of each transfer roller, while a rib engaged with the engaging plate is provided on the inner surface of the transfer belt. In this configuration, the engaging plate and the rib are engaged with each other, thus inhibiting the positional deviation of the transfer belt in the engaging area between the transfer rollers and the transfer belt (more specifically, the engaging area between the supporting plate and the rib).
[Patent Document 1]
Specification of Japanese Patent 2541002
[Patent Document 2]
Publication of Unexamined Japanese Patent Application 11-265124
However, the configurations as described in the above patent documents are aimed at inhibiting the meandering of the transfer belt only in the engaging area between the transfer rollers and the transfer belt, so that meandering of the transfer belt within the image forming area is not always preferably avoided.
In other words for example, if the transfer belt is supported by the transfer rollers only at upstream and downstream locations of the belt, across the image forming area, meandering of the transfer belt is suppressed in the portion of the transfer belt wound around the transfer rollers. However, in the portion of the transfer belt located in the image forming area, the transfer belt often continues to cause the positional deviation by meandering.
If the portion of the transfer belt located in the image forming area continues meandering in this manner and subsequently the positional deviation of the transfer belt in the width direction occurs, the positional deviation of the recording medium fed to the image forming area occurs, and thus the positional deviation of the image forming position occurs.